Abstract

The authors have studied dynamical stability of different polymorphs of using ab initiophonon calculations based on density functional theory in conjunction with force-constant method. Rutile was found stable at ambient pressure, but unstable at high pressure. The calculated Raman frequency and phonon density of states (PDOS) of rutile are in a good agreement with experiment. Concerning two cubic phases (solar materials), fluorite stabilized under pressure, whereas pyrite showed instability throughout the whole pressure range. Furthermore, the PDOS of cotunnite (the hardest known oxide) phase confirmed that it exists at high pressure and can be quenched down to a low pressure limit.

This work is financially supported by the Swedish foundation for International Cooperation in Research and Higher Education (STINT). One of the authors (D.Y.K.) would like to thank B. I. Min’s group for fruitful discussion during visiting POSTECH. Useful discussions with R. Scheicher and M. Mattesini are also acknowledged. The authors also thank the Swedish Research Council (VR) and the Brazilian National Research Council (CNPq) for their support.